The present invention relates to apparatus for covering open top vehicle containers, and, in particular, a hydraulically operated pivoting arm covering system having variable rate actuation.
Governmental regulations require many open vehicle containers carrying particulate and waste cargos to limit spillage during transport. Various mechanical, electrical and hydraulic systems have been proposed for covering the load after filling, and uncovering the load at the discharge site. Hydraulic systems have become preferred for larger containers and vehicles carrying a variety of container sizes.
Typical hydraulic systems, as disclosed in U.S. Pat. Nos. 4,050,734 and 4,341,416 to Richard, and 4,981,317 to Acosta, employ a pair of pivoting arms that unroll a covering tarp over the container top in movement between an open and closed position. The arms are actuated by a hydraulic cylinders controlled by the operator at the side of the vehicle. For long bed containers or vehicles hauling containers of varying sizes, secondary sets of cylinder actuated extendable linkages are employed as shown representatively in U.S. Pat. Nos. 4,874,196 to Horvath; and Re. 36,135 and 6,237,985 to O""Brian.
The hydraulic tarp systems are generally controlled by hydraulic control systems located at the front side of the container behind the vehicle cab. Using two-way valve controls for single actuator sets, or joystick controls for multiple actuator sets, the operator furls or unfurls the cover while maintaining visual contact with its deployment. To minimize deployment time, faster covering rates are preferred by the drivers and the trucking organization. Such speed, however, comes at substantial maintenance costs. The rapid acceleration from the rest condition stresses the cover, the spooling mechanism, and the pivoting arms, and can cause damage to components and misalignments in the system. The impact and sudden deceleration at the end of the cylinder stroke pose similar problems. While slow cylinder rates have been used, the excessive time penalty involved has not been accepted, and accordingly time considerations have prevailed over maintenance preferences.
In view of the foregoing, it would-be desirable to provide a container covering system that would reduce maintenance costs while providing acceptable deployment cycles.
Accordingly it is an object of the present invention to provide a roll-up cover assembly for truck containers that reduces maintenance costs.
Another object of the invention is to provide a hydraulic actuator system for truck container covering apparatus that reduces component damage at the ends of the actuator stroke.
A further object of the invention is to provide a hydraulic actuator for a truck container covering system having reduced initial and terminal actuator rates for reducing equipment damage without significantly reducing overall deployment time.
Yet another object of the invention is to provide a variable rate covering system for open top containers providing controlled extension and retraction rates form open and closed positions.
The foregoing objects are accomplished by a hydraulic actuating system for a pivoting arm container covering system wherein the fluid flow rates to the hydraulic cylinders are reduced during the initial and final phases of the stroke to reduce acceleration and impact forces on the covering system components, and normal fluid flow rates are provided during the central phase, whereby the overall cycle time is not significantly affected. Therein, the hydraulic cylinders are provided with metering orifices that reduce fluid flow rates to and from the cylinder pressure chambers for predetermined portions of the stroke length, thereby cushioning the pivoting mechanism at the terminal positions.